FIG. 1 shows a cross sectional side view of a T-gate device 100. The T-gate device 100 includes a T-gate structure 105 formed on a substrate 125 between a source 115 and a drain 120. The T-gate structure 105 often has a T-shaped gate 105, referred to as simply a T-gate. In general a T-gate is any device which has a narrow gate foot 130 and a relatively wider gate head 110. Sometimes the same or similar structures are referred to as Y-gates and/or mushroom gates due to their final shape. In yet another instance, a gamma-gate or asymmetric gate can be produced. A gamma-gate has a cross section similar to the Greek letter gamma. Accordingly, the terms T-gate, Y-gate, mushroom gate, gamma-gate, and asymmetric gate refer to a tiered gate structure with a narrow gate foot 130 and a relatively wider gate head 110. In this disclosure the term T-gate, the most general and widely used term to refer to such tiered gate structure devices, is intended to encompass all of these structural variations.
T-gate structures, structures with a gate foot 130 smaller than the gate head 110 contact area, can operate at ultra-high frequencies. The T-gate structure allows the source and drain contacts to be moved closer to the gate structure to increase speed and decrease power consumption. Moving the source and drain too close to the gate structure, however, can cause shorts between the source or drain contact and the gate head.
In light of the above, there exists a need for a structure and method of manufacturing to provide a T-gate capable of higher frequency performance without causing shorting between the gate head and the source or drain contact of the T-gate device.